Plasma processing method and plasma processing apparatus

ABSTRACT

Provided are a plasma processing method and a plasma processing apparatus which may form a protective film on the surface of an etching stop layer and suppress clogging of openings of holes when etching an oxide layer are provided. The plasma processing method forms a plurality of holes having different depths in multi-layered films that include an oxide layer, a plurality of etching stop layers made of tungsten, and a mask layer. The plasma processing method includes an etching process in which a processing gas is supplied to generate plasma such that etching is performed from the top surface of the oxide layer to the plurality of etching stop layers so as to form hole having different depths in the oxide layer. Here, the processing gas includes a fluorocarbon-based gas, a rare gas, oxygen, and nitrogen.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of and claims benefit ofpriority from co-pending U.S. application Ser. No. 14/064,293, filedOct. 28, 2013 and also claims the benefit of priority from U.S.Provisional Patent Application No. 61/722,834, filed on Nov. 6, 2012.The present application is further based upon and claims the benefit ofpriority from Japanese Patent Application No. 2012-238072 filed on Oct.29, 2012. The entire contents of foregoing applications are incorporatedherein in their entireties by reference.

TECHNICAL FIELD

The present disclosure relates to a plasma processing method and plasmaprocessing apparatus.

BACKGROUND

A method of etching a multilayer film having an oxide layer is known asa conventional plasma processing method. See, for example, JapanesePatent Laid-Open Publication No. 2005-26659. The method disclosed inJapanese Patent Laid-Open Publication No. 2005-26659 is a manufacturingprocess of a NAND type flash memory and uses a tungsten thin film as ahard mask for etching an oxide layer. The thickness of the tungsten thinfilm is in the range of about 500 Å to 1000 Å such that the tungstenfilm may sufficiently endure as an etching barrier during the subsequentetching of the oxide layer is etched.

Also, Japanese Patent Laid-Open Publication No. 2009-170661 discloses anexample of a NAND type flash memory. This NAND type flash memory has athree-dimensional structure in which memory cells are stacked in thevertical direction in relation to the surface of a semiconductorsubstrate. This memory has multi-layered wiring layers in which aplurality of conductive films and a plurality of insulation films arealternately stacked and contacts configured to supply potentials of wordlines. In order to form the contacts, a plurality of end portions of themulti-layered wiring layers are worked in a step shape. That is, thelengths of the multi-layered wiring layers are set in such a manner thatthe lowermost wiring layer has the longest length and the uppermostwiring layer has the shortest length and thus, the lengths of themulti-layered wiring layers get shorter from the lowermost wiring layertowards the uppermost wiring layer.

SUMMARY

A plasma processing method according to the present disclosure forms aplurality of holes having different depths on multi-layered films usinga plasma processing apparatus including a processing container whichdefines a processing space and a gas supply unit configured to supply aprocessing gas into the processing space. The multilayer film includesan oxide layer and a plurality of etching stop layers. The plurality ofetching stop layers are made of tungsten and disposed below the topsurface of the oxide layer as well as at different positions in alaminating direction. The plasma processing method includes an etchingprocess in which the processing gas is supplied to generate plasma, andetching is performed from the top surface of the oxide layer up to theplurality of etching stop layers so as to simultaneously form aplurality of holes having different depths in the oxide layer. Theprocessing gas includes a fluorocarbon-based gas, a rare gas, oxygen,and nitrogen.

The foregoing summary is illustrative only and is not intended to be inany way limiting. In addition to the illustrative aspects, embodiments,and features described above, further aspects, embodiments, and featureswill become apparent by reference to the drawings and the followingdetailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view schematically illustrating a plasma processingapparatus according to an exemplary embodiment.

FIG. 2 is a schematic perspective view illustrating a NAND type flashmemory having a three-dimensional structure.

FIG. 3 is a cross-sectional view for describing metal contacts.

FIGS. 4A and 4B are schematic views for describing an etching process.

FIG. 5 is a table representing evaluation results of hole shapes,etching resistance of etching stop layers, and clogging with regard toExamples and Comparative Examples.

FIGS. 6A to 6E are views schematically illustrating the hole shapes ofExamples and Comparative Examples.

FIG. 7 is a graph representing evaluation results of the etchingresistance of the etching stop layers in Examples and ComparativeExamples as a relationship between oxygen and nitrogen.

FIG. 8 is a graph representing evaluation results of clogging inExamples and Comparative Examples as a relationship between oxygen andnitrogen.

FIG. 9 is a graph representing a relationship between a flow rate ratioof nitrogen and a flow rate ratio of oxygen.

FIG. 10 is a graph representing optimum flow rates of nitrogen andoxygen.

DETAILED DESCRIPTION

In the following detailed description, reference is made to theaccompanying drawing, which form a part hereof. The illustrativeembodiments described in the detailed description, drawing, and claimsare not meant to be limiting. Other embodiments may be utilized, andother changes may be made without departing from the spirit or scope ofthe subject matter presented here.

In order to form the plurality of contacts disclosed in Japanese PatentLaid-Open Publication No. 2009-170661, it is required to form aplurality of holes having different depths. As for a method for formingthe plurality of holes, for example, the method disclosed in JapanesePatent Laid-Open Publication No. 2005-26659 may be considered in which atungsten layer is disposed on each of the multi-layered wiring layersand an oxide layer formed on the tungsten layer is etched using thetungsten layer as an etching stop layer. By this method, holes havingdifferent depths may be formed simultaneously.

In the method as described above, when the holes are etchedsimultaneously, the holes are sequentially reached to the etching stoplayers from the shallowest hole because the etching stop layers aredisposed at the different positions in the laminating direction.Therefore, the etching stop layer positioned at the bottom of a shallowhole is required to withstand etching until the formation of deeperholes is completed.

However, when over-etching of etching stop layers is avoided byadjusting the thicknesses of the etching stop layers as in the plasmaprocessing method disclosed in Japanese Patent Laid-Open Publication No.2005-26659, it is required to increase the thicknesses of the etchingstop layers according to the depth difference of the holes to be formed.As a result, miniaturization of a device may be hindered. Also, sincethe differences in depth of formable holes are determined according tothe thicknesses of the etching stop layers, a plurality of desired holesmay not be formed.

Therefore, what may be considered is optimizing a processing gas torealize a high selection ratio of the etching stop layers made oftungsten and the oxide layers. For example, using a fluorocarbon-basedgas may be considered as for a processing gas used in the oxide layeretching process. The fluorocarbon-based gas forms a CF-based protectivefilm on the surface of tungsten while generating CF-based radicals whichcontribute to etching of the oxide layers, which results in an excellentselection ratio. Meanwhile, since CF radicals among CF-based radicalsmay become precursors of reaction products which are attached toopenings of the holes, the reaction products may be attached to theopenings of the holes, thereby causing clogging (blocking of theopenings). Thus, using a processing gas containing oxygen may beconsidered so as to remove the reaction products attached to theopenings of the holes. However, since oxygen is gas which has an etchingcharacteristic, it removes the protective films formed on the etchingstop layers. Consequently, the selection ratio of the etching stoplayers and the oxide layers may be reduced.

Therefore, what is desired are a plasma processing method and a plasmaprocessing apparatus which are capable of forming protective films onthe surfaces of etching stop layers and suppressing clogging of theopenings of holes when etching oxide layer.

The inventor the found out that, when nitrogen is used, oxygen supplyamount may be suppressed because the nitrogen affects the productionratio of CF, CF₂, and CF₃ radicals generated from the fluorocarbon-basedgas, which has led to the present disclosure.

A plasma processing method according to the present disclosure forms aplurality of holes having different depths on multi-layered films usinga plasma processing apparatus including a processing container whichdefines a processing space and a gas supply unit configured to supply aprocessing gas into the processing space. The multilayer film includesan oxide layer and a plurality of etching stop layers. The plurality ofetching stop layers are made of tungsten and disposed below the topsurface of the oxide layer as well as at different positions in thelaminating direction. The plasma processing method includes an etchingprocess in which the processing gas is supplied to generate plasma, andetching is performed from the top surface of the oxide layer up to theplurality of etching stop layers so as to simultaneously form aplurality of holes having different depths in the oxide layer. Theprocessing gas includes a fluorocarbon-based gas, a rare gas, oxygen,and nitrogen.

In the method as described above, the processing gas for etching theoxide layer includes a fluorocarbon-based gas, a rare gas, oxygen andnitrogen. When nitrogen is added, CF and CF₃ radicals among CF, CF₂, andCF₃ radicals generated from the fluorocarbon-based gas are reduced. Whenthe CF radicals which are precursors of reaction products attached tothe openings of the holes are reduced, the flow rate of oxygen forremoving the reaction product may be reduced while suppressing theclogging of the openings of the holes. When the flow rate of oxygen isreduced, that the etching of the protective films formed on the etchingstop layers may be avoided. Therefore, the protective films may beformed on the surfaces of the etching stop layers while suppressing theclogging of the openings of the holes when the oxide layer is etched.

In an exemplary embodiment, flow rates of the oxygen and the nitrogenmay be set in such a manner that the plurality of etching stop layersexcept the etching layer which forms the bottom of the deepest hole aresuppressed from being etched and the openings of the plurality of holesare suppressed from being clogged until the etching is performed fromthe top surface of the oxide layer to the surface of the etching stoplayer which forms the bottom of the deepest hole. When the flow rates ofoxygen and nitrogen are set in terms of suppressing the etching of theetching stop layers as described above, holes having different depthsmay be simultaneously formed.

In an exemplary embodiment, when the flow rate of oxygen is set as X(X>0) and the flow rate of nitrogen is set as Y (Y>0), X and Y maysatisfy Y=−5X+b (300 sccm≦b≦375 sccm). In an exemplary embodiment, thenumerical value b may satisfy 325 sccm≦b≦350 sccm and the flow rate ofnitrogen Y may be in the range of 50 sccm≦Y≦100 sccm. When the flowrates of oxygen and nitrogen are set to be in the range of satisfyingthe equation, a high selection ratio of the etching stop layers and theoxide layer may be realized and holes having excellent shapes may beformed.

In an exemplary embodiment, in a multilayer film, a plurality of etchingstop layers may be disposed such that the depth of the deepest hole istwice or more than the shallowest hole. That is, when a NAND type flashmemory having a three-dimensional structure is manufactured, a highselection ratio of the etching stop layers and the oxide layer may berealized and holes having excellent shapes may be formed.

A plasma processing apparatus according to another aspect of the presentdisclosure forms a plurality of holes having different depths on amultilayer film. The multilayer film has an oxide layer and a pluralityof etching stop layers. The plurality of etching stop layers are made oftungsten and disposed below the top surface of the oxide layer in alaminating direction as well as at different positions in the laminatingdirection. The plasma processing apparatus includes a processingcontainer, a mounting table, an upper electrode, a high frequency powersupply, a gas supply system, and a control unit. The mounting table hasa lower electrode and is disposed within the processing container. Theupper electrode is disposed to be opposite to the lower electrode. Thehigh frequency power supply applies high frequency power for excitingplasma to the lower electrode. The gas supply system supplies aprocessing gas that includes a fluorocarbon-based gas, a rare gas,oxygen, and nitrogen into the processing container. The control unitcontrols the gas supply system. The control unit causes the gas supplysystem to supply the processing gas to the processing container togenerate plasma such that etching is performed from the top surface ofthe oxide layer to the plurality of etching stop layers so as tosimultaneously form the plurality of holes having different depths onthe oxide layer.

In the plasma processing apparatus, the processing gas for etching theoxide layer includes a fluorocarbon-based gas, a rare gas, oxygen, andnitrogen. When nitrogen is added, CF radicals and CF₃ radicals arereduced among CF, CF₂, and CF₃ radicals which are generated fromfluorocarbon-based gas. When the CF radicals which are precursors ofreaction products attached to the openings of the holes are reduced,clogging of the openings of the holes may be suppressed and the flowrate of oxygen for removing the reaction products may be reduced. Whenthe flow rate of oxygen is reduced, excessive etching of the protectivefilms formed on the etching stop layers made of tungsten may be avoided.Therefore, when the oxide layer is etched, the protective films may beformed on the surfaces of the etching stop layers and the clogging ofthe openings of the holes may be suppressed.

As described above, a plasma processing method and a plasma processingapparatus which may form protective films on the surfaces of etchingstop layers and suppress clogging of openings of holes when an oxidelayer is etched are provided.

Hereinafter, various exemplary embodiments will be described in detailwith reference to the accompanying drawings. The same symbols will beassigned for the same or equivalent elements in the respective drawings.

FIG. 1 is a view illustrating a plasma processing apparatus according toan exemplary embodiment. The plasma processing apparatus 10 illustratedin FIG. 1 is a capacity coupling type parallel flat plate plasma etchingapparatus and is provided with a processing container 12 which has asubstantially cylindrical shape. For example, the surface of theprocessing container 12 is formed of anodized aluminum. This processingcontainer 12 is protectively grounded.

A cylindrical support unit 14 formed of an insulation material isdisposed on the bottom portion of the processing container 12. Thissupport unit 14 supports a base 16 formed of a metal such as, forexample, aluminum. The base 16 is provided within the processingcontainer 12 and constitutes a lower electrode in an exemplaryembodiment.

An electrostatic chuck 18 is provided on the top surface of the base 16.The electrostatic chuck 18 constitutes a mounting table of the exemplaryembodiment together with the base 16. The electrostatic chuck 18 has astructure in which an electrode 20 which is a conductive film isinterposed between a pair of insulation layers or between a pair ofinsulation sheets. A direct current power supply 22 is electricallyconnected to the electrode 20. The electrostatic chuck 18 may adsorb andmaintain an object to be processed (“workpiece”) W by electrostaticforce such as, for example, Coulomb force generated by a direct currentvoltage from the direct current power supply 22.

A focus ring FR is disposed on the top surface of the base 16 around theelectrostatic chuck 18. The focus ring FR is provided in order toimprove uniformity of etching. The focus ring is formed of a materialwhich is properly selected according to a material of a layer to beetched and may be formed of, for example, silicon or quartz.

A refrigerant chamber 24 is provided inside the base 16. The refrigerantchamber 24 is supplied with a refrigerant of a predeterminedtemperature, for example, cooling water, by circulating the refrigerantvia pipes 26 a, 26 b from a chiller unit provided outside. When thetemperature of the circulated refrigerant is controlled as describedabove, the temperature of the workpiece W mounted on the electrostaticchuck 18 is controlled.

Also, the plasma processing apparatus 10 is provided with a gas supplyline 28. The gas supply line 28 supplies a heat transferring gas from aheat transferring gas supply mechanism, for example, He gas between thetop surface of the electrostatic chuck 18 and the rear side of theworkpiece W.

Further, an upper electrode 30 is provided inside the processingcontainer 12. The upper electrode 30 is located above the base 16 whichis the lower electrode to be opposite to the base 16 and the base 16 andthe upper electrode 30 are provided substantially in parallel to eachother. A processing space S for plasma etching the workpiece W isdefined between the upper electrode 30 and the base (lower electrode)16.

The upper electrode 30 is supported via an insulation shielding member32 at the upper portion of the processing container 12. The upperelectrode 30 may include an electrode plate 34 and an electrode support36. The electrode plate 34 faces the processing space S and defines aplurality of gas ejection holes 34 a. This electrode plate 34 may beconfigured by a low-resistance conductor or a semiconductor which hassmall Joule heat.

The electrode support 36 detachably supports the electrode plate 34 andmay be formed of a conductive material such as, for example, aluminum.The electrode support 36 may have a water-cooled structure. A gasdiffusion chamber 36 a is provided inside the electrode support 36. Aplurality of gas communication holes 36 b that communicate with the gasejection holes 34 a extend downwards from the gas diffusion chamber 36a. Also, the electrode support 36 is formed with a gas inlet 36 cconfigured to introduce the processing gas to the gas diffusion chamber36 a and a gas supply pipe 38 is connected to the gas inlet 36 c.

Gas sources 40 a to 40 d are connected to the gas supply pipe 38 via asplitter 43, valves 42 a to 42 d, and mass flow controllers (“MFC”) 44 ato 44 d. Meanwhile, a flow control system (“FCS”) may be provided,instead of MFC. The gas source 40 a is a gas source of a processing gasthat includes a fluorocarbon-based gas (C_(x)F_(y)) such as, forexample, C₄F₆ and C₄F₈ gases. The gas source 40 b is a gas source of aprocessing gas that includes a rare gas such as, for example, Ar gas.The gas source 40 c is a gas source of a processing gas that includes,for example, oxygen. The gas source 40 d is a gas source of a processinggas that includes, for example, nitrogen. Upon reaching the gasdiffusion chamber 36 a from the gas supply pipe 38, the processing gasesfrom the gas sources 40 a to 40 d are ejected to the processing space Svia the gas communication holes 36 b and the gas ejection holes 34 a.The gas sources 40 a to 40 d, the valves 42 a to 42 d, the MFC 44 a to44 d, the splitter 43, the gas supply pipe 38, and the upper electrode30 which defines the gas diffusion chamber 36 a, the gas communicationholes 36 b and gas ejection holes 34 a constitute a gas supply unit inthe exemplary embodiment.

Also, the plasma processing apparatus 10 may be further provided with aground conductor 12 a. The ground conductor 12 a has a substantiallycylindrical shape and is provided so as to extend upwards from a sidewall of the processing container 12 to a position higher than the heightof the upper electrode 30.

Further, in the plasma processing apparatus 10, a deposition shield 46is detachably provided along the inner wall of the processing container12. The deposition shield 46 is also provided on the outer circumferenceof the support unit 14. The deposition shield 46 is configured toprevent a byproduct of etching (deposition) from being attached to theprocessing container 12 and may be formed by covering an aluminummaterial with ceramics such as, for example, Y₂O₃.

In the bottom portion side of the processing container 12, an exhaustplate 48 is provided between the support unit 14 and the inner wall ofthe processing container 12. The exhaust plate 48 may be formed bycovering an aluminum material with ceramics such as, for example, Y₂O₃.The processing container 12 is formed with an exhaust port 12 e belowthe exhaust plate 48. An exhaust device 50 is connected to the exhaustport 12 e via an exhaust pipe 52. Since the exhaust device 50 has avacuum pump such as, for example, a turbo molecule pump, the inside ofthe processing container 12 may be depressurized to a desired degree ofvacuum. The exhaust device 50 maintains the inside of the processingcontainer 12 at the degree of vacuum of, for example, 20 mTorr to 40mTorr (2.66 Pa to 5.32 Pa). The side wall of the processing container 12is formed with a carry-in/out port 12 g of a workpiece W and thecarry-in/out port 12 g is configured to be opened/closed by a gate valve54.

A conductive member (GND block) 56 is provided on the inner wall of theprocessing container 12. The conductive member 56 is attached to theinner wall of the processing container 12 to be positioned at the heightwhich is substantially the same as that of the workpiece W in the heightdirection of the conductive member 56. The conductive member 56 isconnected to a ground in a DC-like manner so as to exhibit an abnormalelectric discharge preventing effect. Meanwhile, the conductive member56 may be installed in the plasma generating region and the installationposition thereof is not limited to the position illustrated in FIG. 1.For example, the conductive member 56 may be provided at the base 16side, for example, around the base 16. Also, the conductive member 56may be provided in the vicinity of the upper electrode 30, for example,on the outer periphery of the upper electrode 30 in a ring shape.

In an exemplary embodiment, the plasma processing apparatus 10 isfurther provided with a power supply rod 58 configured to supply thehigh frequency power to the base 16 that constitutes the lowerelectrode. The power supply rod 58 constitutes a power supply lineaccording to the exemplary embodiment. The power supply rod 58 has acoaxial double pipe structure and includes a rod-shaped conductivemember 58 a and a cylinder-shaped conductive member 58 b. The rod-shapedconductive member 58 a extends substantially vertically from the outsideof the processing container 12 to the inside of the processing container12 through the bottom portion of the processing container 12 and theupper end of the rod-shaped conductive member 58 is connected to thebase 16. Also, the cylinder-shaped conductive member 58 b is coaxialwith the rod-shaped conductive member 58 a such that it surrounds therod-shaped conductive member 58 a. The cylinder-shaped conductive member58 b is supported on the bottom portion of the processing container 12.Two pieces of substantially annular insulation members 58 c areinterposed between the rod-shaped conductive member 58 a and thecylinder-shaped conductive member 58 b to electrically insulate therod-shaped conductive member 58 a and the cylinder-shaped conductivemember 58 b.

Also, in an exemplary embodiment, the plasma processing apparatus 10 maybe further provided with matching devices 70, 71. The matching devices70, 71 are connected with the lower ends of the rod-shaped conductivemember 58 a and the cylinder-shaped conductive member 58 b. Also, thematching devices 70, 71 are connected with a first high frequency powersupply 62 and a second high frequency power supply 64, respectively. Thefirst high frequency power supply 62 is configured to generate a firsthigh frequency (RF: Radio Frequency) power with a frequency of 27 MHz to100 MHz, for example, 40 MHz. The first high frequency power is 1000 Wto 2000 W, for example. The second high frequency power supply 64applies a high frequency bias to the base 16 to generate a second highfrequency power for attracting ions to a workpiece W. The frequency ofthe second high frequency power is in the range of 400 kHz to 13.56 MHz,for example, 3 MHz. Also, the second high frequency power is 3000 W to5000 W, for example. In addition, a direct current power supply 60 isconnected to the upper electrode 30 via a low pass filter. The directcurrent power supply 60 outputs a minus direct current voltage to theupper electrode 30. By the configuration described above, two differenthigh frequency powers may be supplied to the base 16 that constitutesthe lower electrode, thereby applying a direct current voltage to theupper electrode 30.

In an exemplary embodiment, the plasma processing apparatus 10 may befurther provided with a control unit Cnt. The control unit Cnt is acomputer that includes, for example, a processor, a storage unit, aninput device, and a display and controls each units of the plasmaprocessing apparatus 10, for example, a power supply system, a gassupply system, and a drive system. In the control unit Cnt, an operatormay, for example, perform an input operation of a command in order tomanage the plasma processing apparatus 10 using the input device and thedisplay may visualize and display an operation state of the plasmaprocessing apparatus 10. Furthermore, the storage unit of the controlunit Cnt is stored with a control program for controlling variousprocessings which are executed in the plasma processing apparatus 10 bythe processor or a program for executing a processing in eachconstitutional element of the plasma processing apparatus 10 accordingto a processing condition, that is, a processing recipe.

When etching is performed using the plasma processing apparatus 10, aworkpiece W is mounted on the electrostatic chuck 18. The workpiece Wmay have a layer to be etched and a resist mask provided on the layer tobe etched. Then, the processing gases from the gas supplies 40 a to 40 dare supplied into the processing container 12 at a predetermined flowrate while the inside of the processing container 12 is being exhaustedby the exhaust device 50 and the inner pressure of the processingcontainer 12 is set to be, for example, in the range of 0.1 Pa to 50 Pa.

Subsequently, the first high frequency power supply 62 supplies thefirst high frequency power to the lower electrode 16. Also, the highfrequency power supply 64 supplied the second high frequency power tothe lower electrode 16. Furthermore, the direct current power supply 60supplies the first direct current voltage to the upper electrode 30.Accordingly, a high frequency electric field is formed between the upperelectrode 30 and the lower electrode 16 to plasmarize the processinggases supplied to the processing space S. The layer to be etched of theworkpiece W is etched by positive ions and radicals generated by theplasma.

Next, a workpiece W which is etched by the plasma processing apparatus10 will be described in detail. The workpiece W is used to form astructure of a NAND type flash memory having multilayered films of, forexample, a three-dimensional structure. FIG. 2 is a schematic viewillustrating the NAND type flash memory. As illustrated in FIG. 2,multi-layered wiring layers 200 have metal contacts MC1 to MC4configured to supply potentials of word lines, respectively. In order toform the metal contacts, a plurality of end portions of themulti-layered wiring layers 200 are worked in a step shape. FIG. 3 is aschematic cross-sectional view illustrating a portion where the metalcontacts MC1 to MC4 are formed. As illustrated in FIG. 3, of themulti-layered wiring layers 200 a to 200 d has, for example, aninsulation layer 101 a, 101 b, 101 c, or 101 d and a conductive film 100a, 100 b, 100 c, or 100 d. The lengths of the multi-layered wiringlayers 200 are set in such a manner that the lowermost wiring layer 200d has the longest length and the uppermost wiring layer 200 a has theshortest length. The lengths of the multi-layered wiring layers 200 a to200 d get shorter from the lowermost wiring layer 200 d towards theuppermost wiring layer 200 a. An insulation layer 102, a buffer film103, and an amorphous carbon layer (“ACL”) 104 are formed on the top ofeach of the multi-layered wiring layers 200 a to 200 d. The metalcontacts MC1 to MC4 are formed by depositing a conductive material suchas, for example, a metal, into holes H1 to H4 formed on the ACL 104, thebuffer film 103, and the insulation layer 102. The holes H1 to H4 aresimultaneously formed when the insulation layer 102 and the buffer film103 are etched using the conductive films 100 a to 100 d as base layers(etching stop layers) and the depths thereof are different from oneanother.

The etching process that simultaneously forms the holes having differentdepths described above will be described using a schematic view wherethe structure is simplified. FIGS. 4A and 4B are schematic views fordescribing the etching process of the plasma processing method. Asillustrated in FIG. 4A, a workpiece W has a substrate 99, an insulationlayer (oxide layer) 105, an ACL 104, and a hard mask 107 such as, forexample, SiNO. The insulation layer 105 is formed on the substrate 99using, for example, SiO₂. The etching stop layers (conductive films) 100a, 100 b are disposed at different positions in the laminating directioninside the insulation layer 105. For example, the etching stop layer 100a is positioned at depth D3 from a top surface 105 a of the insulationlayer 105 and the etching stop layer 100 b is positioned at depth D5from the top surface 105 a of the insulation layer 105. That is, theetching stop layers 100 a, 100 b are disposed below the top surface 105a of the insulation layer 105 in the laminating direction. For example,depth D3 is about 1000 nm to 1500 nm and depth D5 is about 3000 nm to3500 nm. That is, the plurality of simultaneously formed holes may havedifferent depths and the depth of a hole may be two or more times asdeep as that of another hole. For example, tungsten (W) is used as theetching stop layers and the thicknesses of the etching stop layers are,for example, about 30 nm to 80 nm.

The ACL 104 and the hard mask 107 are disposed as a mask layer above thetop surface 105 a of the insulation layer 105 in the laminatingdirection. The ACL 104 and the hard mask 107 have openings K1, K2 ofdiameter D2 formed at the positions which overlap the plural etchingstop layers 100 a, 100 b when viewed in the laminating direction,respectively. Here, the height of the mask layer is, for example, 1000nm to 1500 nm and the diameters of the openings K1, K2 are 50 nm to 100nm.

Subsequently, as illustrated in FIG. 4B, the mask layer and the etchingstop layers 100 a, 100 b are used to simultaneously etch plural holesH1, H2 having different depths in the insulation layer 105. Here, as forthe processing gas for etching the insulation layer 105, a processinggas that includes a fluorocarbon-based gas, a rare gas, oxygen, andnitrogen is employed. In an exemplary embodiment, when the flow rate ofoxygen is set as X (X>0) and the flow rate of nitrogen is set as Y(Y>0), X and Y may satisfy Y=−5X+b (300 sccm≦b≦375 sccm). Also, in anexemplary embodiment, the numerical value b may satisfy 325 sccm≦b≦350sccm and the flow rate of oxygen and the flow rate of nitrogen may beadjusted such that the flow rate of nitrogen Y is 50 sccm≦Y≦100 sccm.

The fluorocarbon-based gas contributes to etching an oxide layer and CF,CF₂, and CF₃ radicals are generated from the fluorocarbon-based gas.Here, when nitrogen is added, the CF radicals and the CF₃ radicals arereduced among CF, CF₂, and CF₃ radicals generated from thefluorocarbon-based gas. The CF radicals are precursors of reactionproducts attached to the openings of the holes. When the CF radicals arereduced, clogging (blockage of the openings of the holes) is suppressed,necking of the holes is improved, and bowing is improved. As a result,the holes H1, H2 having excellent shapes may be formed. When nitrogen isadded, reaction products attached to the openings of the holes arereduced. Therefore, the flow rate of oxygen for removing the reactionproducts may be reduced. By reducing the flow rate of oxygen, excessiveetching of the protective films formed on the etching stop layers 100 a,100 b is avoided. Thus, the etching stop layers 100 a, 100 b maywithstand etching for a long time. As described above, the flow rate ofoxygen and the flow rate of nitrogen are set in such a manner that theetching of the etching stop layer 100 a except the etching stop layer100 b which is the bottom of the deepest hole H2 from the top surface105 a of the insulation layer 105 to the surface of the etching stoplayer 100 b which is the bottom of the deepest hole H2 is suppressed andthe clogging of the openings of the plural holes H1, H2 is alsosuppressed until the etching is performed from the top surface 105 a ofthe insulation layer 105 to the surface of the etching stop layer 100 bwhich is the bottom of the deepest hole H2. Therefore, when theprotective films are formed on the surfaces of the etching stop layers100 a, 100 b, a high selection ratio of the etching stop layers 100 a,100 b, and the insulation layer 105 may be realized and the holes H1, H2having the excellent shapes may be formed while suppressing the cloggingof the holes H1, H2.

Meanwhile, actions resulted from introducing nitrogen are not limited tothe foregoing and actions set forth below may occur in combination.

For example, CF₂ radicals form the protective film of tungsten at thebottom of the hole. Even when nitrogen is added, the CF₂ radicals tendnot to be reduced as compared with the CF and CF₃ radicals. Thus, whennitrogen is added, the CF radicals are reduced, the attachment ofdeposition to the openings of the holes is reduced, necking is improved,and CF₂ radicals reach the bottoms of the holes easily. As a result, itis thought that a good protective film is formed on each of the surfacesof tungsten layers which are the etching stop layers. Or, it is alsothought that a CN-based protective film having higher etching resistancethan that of a CF-based protective film is formed on the surfaces oftungsten surfaces which are the etching stop layers.

The first ionization energies of O, N, O₂, and N₂ are 13.618 eV, 14.53eV, 12.07 eV, and 15.58 eV, respectively. Thus, O is easily ionized ascompared to N and O ions may be easily drawn into the bottoms of holes.Therefore, when a large amount of O exists, it is thought that theprotective films of the surfaces of the tungsten layers which are theetching stop layer tend to be easily etched. Meanwhile, it is thoughtthat since N is hardly ionized as compared to O, the ratio of N actingas radicals increases and N participates in the removal of deposition ofthe openings of the holes rather than the bottoms of the holes. Also, Nradicals have a higher attachment coefficient as compared to O radicals.Thus, it is thought that the N radicals hardly reach the bottom of theholes since they react with the deposition of the openings of the holes.Therefore, it is thought that a good hole shape and a high selectionratio may be realized when nitrogen is introduced and the ratio ofoxygen is reduced.

Although various exemplary embodiments have been described above, thepresent disclosure is not limited thereto and may constitute variousmodified aspects. For example, in the exemplary embodiments as describedabove, two high frequency power supplies are connected to the lowerelectrode 16. However, the first high frequency power supply may beconnected to one of the lower electrode 16 and the upper electrode 30and the second high frequency power supply may be connected to the otherelectrode.

EXAMPLES

Hereinafter, examples and comparative examples carried out by thepresent inventor will be described.

Examples 1 to 7

A SiO₂ layer which is an insulation layer was formed on a tungsten layerwhich is an etching stop layer, a mask constituted with a hard masklayer and an ACL was formed, and a hole was formed by etching under thefollowing conditions.

[Etching Conditions]

Flow Rate of Gas

C₄F₆ gas: 50 sccm

Ar gas: 600 sccm

O₂ gas: 45 sccm to 60 sccm

N₂ gas: 50 sccm to 100 sccm

Processing time: 380 sec

Here, the flow rates of O₂ gas and N₂ gas were 60 sccm and 50 sccm,respectively, in Example 1, 55 sccm and 50 sccm in Example 2, 50 sccmand 50 sccm in Example 3, 60 sccm and 100 sccm in Example 4, 55 sccm and100 sccm in Example 5, 50 sccm and 100 sccm in Example 6, and 45 sccmand 100 sccm in Example 7.

Comparative Examples 1 and 2

In Comparative Examples 1 and 2, etching was performed using aprocessing gas which does not include nitrogen. The flow rate of O₂ gasas an etching condition was 65 sccm in Comparative Example 1 and 60 sccmin Comparative Example 2. Other conditions were the same as those ofExamples 1 to 7.

(Other Processes)

In Comparative Example 1, 2 and Examples 1 to 7, an ashing process forthe insulation layer and an ashing process for the etching stop layerwere performed.

(Results)

FIG. 5 is a table representing the results of evaluating a hole shape,etching resistance of etching stop layers, and clogging in Examples 1 to7 and Comparative Examples 1 and 2 are evaluated. In FIG. 5, ComparativeExamples 1 and 2 and Examples 1 to 7 are indicates as numbers. Targetrefers to a target value (reference value). The values were determinedfrom SEM images. Details of the results represented in FIG. 5 areillustrated in FIGS. 6 to 8.

(Evaluation of Hole Shape)

Firstly, the hole shape was evaluated based on whether the ACL which isa mask of an insulation layer was etched or not, the thickness of theACL after etching, and the selection ratio of the SiO₂ layer and theACL. As illustrated in FIG. 5, it was confirmed that although the ACLwas somewhat etched in Examples 4 and 5, the ACL with the thickness of,for example, 254 nm or 351 nm remained and enough film thickness as amask remained. Also, it was confirmed that the target depth of the holedepth of 3000 nm to 3200 nm was achieved in Comparative Example 1 andExamples 1, 2, 4, 5 and 6. Subsequently, after the ashing process forthe insulation layer, a width in the vicinity of the opening of the holeTop, the maximum width of the hole Bow, and a difference Δ(Bow-Top) weremeasured. As illustrated in FIG. 5, it was confirmed that the differenceΔ(Bow-Top) in Comparative Example 1 was 51 and the hole shape was notgood. Meanwhile, the difference Δ(Bow-Top) in Examples 1, 2, 4, 5 and 6was in the range of 6 to 32. Therefore, it was confirmed that the holeshapes becomes good as an effect of adding nitrogen. Subsequently, theashing process for the etching stop layer was performed and a width inthe vicinity of the opening of the hole Top, a width of the bottom Btm,and the maximum width of the hole Bow were measured. The results wererepresented in FIGS. 6A to 6E. FIGS. 6A to 6E are views schematicallyillustrating the images of cross-sectional SEM images of ComparativeExample 1 and Examples 1 and 4 to 5. As illustrated in FIGS. 6A to 6E,the width in the vicinity of the opening of the hole Top, the width ofthe bottom Btm, and the maximum width of the hole Bow were measured. Asapparent from Top values and Bow values represented in FIGS. 6A to 6E,it was confirmed that the difference Δ(Bow-Top) is smaller in Examples1, 4, 5 and 6 as compared to Comparative Example 1. Therefore, it wasreconfirmed that the hole shape becomes good as an effect of addingnitrogen.

(Evaluation of Etching Resistance of Etching Stop Layer)

After the ashing process for the etching stop layer, a loss of atungsten layer which is an etching stop layer (the etched depth from thestop surface of the tungsten layer) and a selection ratio (SiO₂/W) wereevaluated. As illustrated in FIG. 5, it was confirmed that the loss ofthe tungsten layer was reduced in Examples 1, 2, 4, 5 and 6 as comparedto Comparative Example 1 and the selection ratio was large in Examples1, 2, 4, 5, 6 as compared to Comparative Example 1. FIG. 7 is a graphillustrating schematic views of the cross-section SEM images inComparative Example 1 and Examples 1, 2, 4, 5 and 6 after the values ofFIG. 5 were confirmed and a relationship of the flow rate of oxygen andthe flow rate of nitrogen. The horizontal axis is the flow rate ofoxygen and the vertical axis is the flow rate of nitrogen. Asillustrated in FIG. 7, it was confirmed that the loss of the tungstenlayer is reduced as the amount of oxygen decreases.

(Evaluation of Clogging)

It was visually confirmed whether clogged holes exist or not among 132holes of the photographed SEM images before the ashing process. Theresults are illustrated in FIG. 5. Meanwhile, when no clogged holeexists, the result is indicated as Free. As illustrated in FIG. 5,clogging was confirmed in Comparative Example 2 and Example 3. Noclogged holes existed in Comparative Example 1 and Examples 1, 2, 4, 5,6 and 7. FIG. 8 is a graph illustrating schematic views of ComparativeExamples 1 and 2 and Examples 1 to 7 and the relationship of the flowrate of oxygen and the flow rate of nitrogen. The horizontal axis is theflow rate of oxygen and the vertical axis is the flow rate of nitrogen.In the schematic views, holes H viewed from the top side are depictedand the portions indicated by substantially circular shapes are portionsopened as the holes H. Gray holes are holes where clogging occurred. Asillustrated in FIG. 8, it was confirmed that clogging is improved as theamount of nitrogen and the amount of oxygen increase.

(Relationship of Flow Rate of Oxygen and Flow Rate of Nitrogen)

FIG. 9 is a graph illustrating a tendency obtained from experimentalresults illustrated in FIGS. 5 to 8 and the horizontal axis is the flowrate of oxygen and the vertical axis is the flow rate of nitrogen. Asillustrated in FIG. 9, it can be seen that clogging is improved when theflow rate of nitrogen is increased. Also, it can be seen that the lossof the tungsten layer is improved while clogging deteriorates when theamount of oxygen decreases. Thus, it can be seen that there is arelationship of oxygen and nitrogen for solving trade-off between theloss of the tungsten layer and clogging. FIG. 10 illustrated theexamined relationship in detail. FIG. 10 is a graph representing atendency obtained from the test results illustrated in FIGS. 5 to 8 indetail and the horizontal axis is the flow rate of oxygen and thevertical axis is the flow rate of nitrogen. The black circles in FIG. 10represent a condition in which both the loss of the tungsten layer andclogging were improved, the black triangles represent a condition inwhich clogging occurred, and the white triangles represent a conditionin which the loss of tungsten layer occurred. That is, in the shadedregion in the figure, the flow rate of oxygen and the flow rate ofnitrogen solve the trade-off between the loss of the tungsten layer andclogging. This region may be defined based on the distance from thesolid line depicted in the figure. From the test results, when the flowrate of oxygen was set as X (X>0) and the flow rate of nitrogen was setas Y (Y>0), X and Y satisfied Y=−5X+b (300 sccm≦b≦375 sccm). Also, itwas found out that the numerical value b may satisfy 325 sccm≦b≦350 sccmand the flow rate of nitrogen may be 50 sccm≦Y≦100 sccm. As describedabove, a relationship of the flow rate of oxygen and the flow rate ofnitrogen which is capable of forming the protective film on the surfaceof an etching stop layer and suppressing the clogging of the openings ofholes was specified.

From the foregoing, it will be appreciated that various embodiments ofthe present disclosure have been described herein for purposes ofillustration, and that various modifications may be made withoutdeparting from the scope and spirit of the present disclosure.Accordingly, the various embodiments disclosed herein are not intendedto be limiting, with the true scope and spirit being indicated by thefollowing claims.

What is claimed is:
 1. A plasma processing apparatus comprising: aprocessing container; a mounting table having a lower electrode anddisposed within the processing container; an upper electrode disposed tobe opposite to the lower electrode; a high frequency power supplyconfigured to applies a high frequency power for exciting plasma to thelower electrode; a gas supply system configured to supply a processinggas that includes a fluorocarbon-based gas, a rare gas, oxygen, andnitrogen within the processing container; and a control unit configuredto control the gas supply system, wherein the control unit causes thegas supply system to supply the processing gas to the processingcontainer so as to generate plasma such that etching is performed onmulti-layered films which include an oxide layer and a plurality ofetching stop layers, the etching stop layers being made of tungsten anddisposed below the top surface of the oxide layer in a laminatingdirection as well as at different positions in the laminating direction,from the top surface of the oxide layer to the plurality of etching stoplayers so as to simultaneously form a plurality of holes havingdifferent depths in the oxide layer.
 2. The plasma processing apparatusof claim 1, wherein flow rates of the oxygen and the nitrogen are set insuch a manner that the plurality of etching stop layers except theetching stop layer which is a bottom of the deepest hole are suppressedfrom being etched and openings of the plurality of holes are alsosuppressed from being clogged until the etching is performed from thetop surface of the oxide layer to the surface of the etching stop layerwhich forms the bottom of the deepest hole.
 3. The plasma processingapparatus of claim 1, wherein, when a flow rate of the oxygen is set asX (X>0) and a flow rate of the nitrogen is set as Y (Y>0), X and Ysatisfies Y=−5X+b (300 sccm≦b≦375 sccm).
 4. The plasma processingapparatus of claim 3, wherein the numerical value b satisfies 325sccm≦b≦350 sccm and the flow rate of the nitrogen Y is 50 sccm≦Y≦100sccm.
 5. The plasma processing apparatus of claim 1, wherein in themulti-layered films, the plurality of etching stop layers are disposedsuch that the depth of the deepest hole is twice or more than the depthof the shallowest hole.